The present invention is a process for the modification of a hydrogenation catalyst of the Raney nickel, Raney cobalt, nickel-on-carrier, or cobalt-on-carrier type.
As a consequence of the process, in which such a catalyst is treated with carbon monoxide, carbon dioxide, formaldehyde, a lower aliphatic aldehyde, an aromatic aldehyde, an aliphatic ketone, an aromatic ketone, a mixed aliphatic/aromatic ketone, glyoxal, pyruvaldehyde or glyoxylic acid, when the thus-modified catalyst is used in the hydrogenation of a nitrile to the corresponding amine the selectivity is increased. The increased selectivity favors significantly the amount of the primary amine vis-à-vis the undesired secondary amine in the hydrogenation product compared with the case when the corresponding unmodified catalyst is employed. The mode of the modification and the increased selectivity resulting therefrom are surprising. Accordingly, the present invention concerns, in a second aspect, a process for the hydrogenation of a nitrile to the corresponding primary amine using a thus-modified catalyst.
One embodiment of the invention is a process for modifying a hydrogenation catalyst of a Raney nickel, Raney cobalt, nickel-on-carrier or cobalt-on-carrier type. This process includes providing a hydrogenation catalyst of the Raney nickel, Raney cobalt, nickel-on-carrier, or cobalt-on-carrier type; and treating the hydrogenation catalyst at temperatures of about 0xc2x0 C. to about 120xc2x0 C. with a modification agent selected from the group consisting of carbon monoxide, carbon dioxide, formaldehyde, a lower aliphatic aldehyde, an aromatic aldehyde, an aliphatic ketone, an aromatic ketone, a mixed aliphatic/aromatic ketone, glyoxal, pyruvaldehyde, and glyoxylic acid in a liquid dispersion medium consisting of water or an organic solvent for about 15 minutes to about 24 hours.
Another embodiment of the invention is a process for the catalytic hydrogenation of a nitrile to its corresponding primary amine. This process includes providing a modified hydrogenation catalyst formed by treating a hydrogenation catalyst selected from the group consisting of a Raney nickel, Raney cobalt, nickel-on-carrier, and cobalt-on-carrier type catalyst at temperatures of about 0xc2x0 C. to about 120xc2x0 C. with a modification agent selected from the group consisting of carbon monoxide, carbon dioxide, formaldehyde, a lower aliphatic aldehyde, an aromatic aldehyde, an aliphatic ketone, an aromatic ketone, a mixed aliphatic/aromatic ketone, glyoxal, pyruvaldehyde, and glyoxylic acid in a liquid dispersion medium consisting of water or an organic solvent for a duration of about 15 minutes to about 24 hours; and contacting a nitrile with the modified hydrogenation catalyst to catalyze the reaction of the nitrile to its corresponding primary amine.
The process in accordance with the invention for the modification of a hydrogenation catalyst of the Raney nickel, Raney cobalt, nickel-on-carrier or cobalt-on-carrier type includes treating the hydrogenation catalyst at temperatures of about 0xc2x0 C. to about 120xc2x0 C. with carbon monoxide, carbon dioxide, formaldehyde, a lower aliphatic aldehyde, an aromatic aldehyde, an aliphatic ketone, an aromatic ketone, a mixed aliphatic/aromatic ketone, glyoxal, pyruvaldehyde, or glyoxylic acid as the modification agent in a liquid dispersion medium consisting of water or an organic solvent for about 15 minutes to about 24 hours.
When the modification agent is formaldehyde, it can also be used in the form of metaldehyde or paraformaldehyde. Preferably, formaldehyde is used in the form of its aqueous solution, i.e. as formalin, in which case water then forms at least part of the liquid dispersion medium.
The xe2x80x9clower aliphatic aldehydexe2x80x9d which can be used as the modification agent in the present invention is preferably an aldehyde of the formula R1CHO in which R1 is an alkyl group with 1 to 5 carbon atoms optionally substituted with hydroxy. The alkyl group can be straight-chained or branched depending on the number of carbon atoms. In the case where the alkyl group is substituted with hydroxy, one or more hydroxy substituents can be present. Preferably, acetaldehyde is used as such a modification agent.
The xe2x80x9caromatic aldehydexe2x80x9d which can be used as the modification agent in the present invention is especially an aldehyde of the formula R2CHO in which R2 is an aryl or heteroaryl group. The term xe2x80x9carylxe2x80x9d as used herein embraces not only the usual unsubstituted aryl groups, i.e. phenyl and naphthyl, but also the corresponding substituted phenyl and naphthyl groups. The substituents may be, for example, halogen atoms and C1-4-alkyl, hydroxy, C1-4-alkoxy, amino, carbamoyl, and phenyl groups; in each case one or more substituents can be present. Fluorine, chlorine, bromine, or iodine is to be understood under the term xe2x80x9chalogen.xe2x80x9d An alkyl or alkoxy group can be straight-chain or branched depending on the number of carbon atoms. In the case of multiple substituents the substituents may be the same or different. Normally, not more than 5 (for phenyl) or 7 (for naphthyl) halogen atoms, 3 alkyl groups, 2 hydroxy groups, 3 alkoxy groups, 2 amino groups, 2 carbamoyl groups, or one phenyl group may be present as a substituent. The term xe2x80x9cheteroarylxe2x80x9d as used herein embraces heteroaryl groups which have one or more hetero atoms in the ring, such as nitrogen, oxygen, and/or sulphur atoms; pyridyl and pyrimidinyl are examples of such heteroaryl groups. Preferably, benzaldehyde or anisaldehyde is used as the aromatic aldehyde in the role of the modification agent.
The xe2x80x9caliphatic, aromatic or mixed aliphatic/aromatic ketonexe2x80x9d which can be used as the modification agent in the present invention is preferably a ketone of the formula R3COR4 in which R3 and R4 each independently signify an alkyl, aryl, or heteroaryl group. The term xe2x80x9calkyl,xe2x80x9d xe2x80x9caryl,xe2x80x9d or xe2x80x9cheteroarylxe2x80x9d as used herein are to be understood as above in connection with the definitions of R1 and R2. Preferably, acetone is used as such a modification agent.
In one embodiment of the invention carbon monoxide, formaldehyde or a lower aliphatic aldehyde is used as the modification agent.
The hydrogenation catalysts of the Raney nickel and Raney cobalt type which can be modified in the modification process in accordance with the invention are well known to a person skilled in the art and are readily obtainable commercially. The same applies to the catalysts of the nickel-on-carrier and cobalt-on-carrier type which likewise can be modified in the process. The carrier in these two cases may be, for example, silica, titanium oxide, aluminum oxide, kieselguhr, or active carbon.
Suitable organic solvents in which, in addition to water, the modification may be carried out include aliphatic hydrocarbons (e.g. pentane and hexane), aromatic hydrocarbons (e.g. benzene and toluene), alkanols (e.g. methanol, ethanol, and propanol), aliphatic and cyclic ethers (e.g. diethyl ether and, respectively, tetrahydrofuran, and dioxan), as well as heteroaromatics (e.g. pyridine). The dispersion medium can consist of water alone or of a single organic solvent or of two or more of such liquids. For example, an aqueous alkanol, e.g. aqueous ethanol, can be used as the liquid dispersion medium. In general, the process is carried out by dispersing the hydrogenation catalyst in water and/or such an organic solvent, because a dissolution of the catalyst does not take place due to its nature. On the other hand, the modification agent must at least partially dissolve in the dispersion medium, as will be explained in more detail below.
Based on the amount of hydrogenation catalyst to be modified, the amount of modification agent which is employed is as follows in the different cases:
The amount of dispersion medium employed must be enough to disperse the hydrogenation catalyst so that the modification agent can act on the catalyst efficiently. The amount to be used depends on many factors, such as, for example, the design of the reactor and the rotation speed of a stirrer which is used, and can be readily established by a person skilled in the art by appropriate experimentation.
The temperature range in which the modification process in accordance with the invention is carried out is from about 0xc2x0 C. to about 120xc2x0 C. Preferably, the process is carried out at room temperature.
Depending on the modification agent and liquid dispersion medium used, on the amount of modification agent employed, as well as on the temperature at which the modification process is carried out, the modification agent can exert its effect in completely dissolved or partially dissolved form. For example, formaldehyde is usually employed in dissolved form, namely in an aqueous solution (as formalin), whereas paraformaldehyde is preferably employed in an almost undissolved (solid) form. During the modification process, the modification agent must be dispersed in the dispersion medium as homogeneously as possible (usually by adequate intermixing); this is especially important when the modification agent, such as, for example, carbon monoxide or paraformaldehyde, has a poor or only limited solubility in the dispersion medium. For this purpose stirring or shaking is preferably performed during the modification process in order to promote homogeneous distribution.
Furthermore, it is advantageous to avoid as far as possible contact of the hydrogenation catalyst with oxygen by the use of an inert gas, e.g. nitrogen or argon. In this manner, undesired deactivation of the catalyst is minimized.
As mentioned above, when the hydrogenation catalyst modified in accordance with the invention is used in a hydrogenation of a nitrile a surprisingly good selectivity in favor of the corresponding primary amine is achieved. In the present reaction, less byproducts, especially less secondary and tertiary amines, are produced as compared to when the corresponding unmodified hydrogenation catalyst is employed. The increase in selectivity is achieved with the activity of the hydrogenation catalyst remaining unchanged. Consequently, hydrogenation of nitrites can be carried out more efficiently.
A further advantage of the hydrogenation catalyst modified in accordance with the invention is that, after the modification it can be stored under water for a long time, i.e., for at least 30 days, without its activity and selectivity being lost. Therefore, the use of the modified catalyst in a hydrogenation need not be undertaken immediately after its modification.
Another process in accordance with the invention is the use of the hydrogenation catalyst modified in accordance with the invention to catalytically hydrogenate a nitrile to the corresponding primary amine. This process includes using as the hydrogenation catalyst one which has been obtained in accordance with the modification process defined above.
The hydrogenation catalyst modified in accordance with the invention which is to be used can be employed either after isolation from the mixture obtained after completion of the modification process or immediately and without isolation in this mixture.
To isolate it, the modified catalyst can be washed by sedimentation or filtration and suspension with fresh dispersion medium or rinsing of the filter cake. The same solvent can be used for the modification process as that which is usually used for the subsequent hydrogenation, so that in the second case an intermediary stage supplementation of the amount of solvent may be required. In this case, however, it is important that the modification agent is consumed, i.e. is no longer detectable, in order to avoid side reactions in the subsequent hydrogenation.
In principle, all nitrites can be hydrogenated selectively to their corresponding primary amines by the hydrogenation process in accordance with the invention. In particular, aliphatic nitrites, e.g. alkyl and alkenyl nitrites, aryl nitrites as well as heteroaryl nitrites may be hydrogenated. The term xe2x80x9carylxe2x80x9d as used herein embraces not only the usual unsubstituted aryl groups, i.e. phenyl and naphthyl, but also corresponding substituted phenyl and naphthyl groups as are illustrated in more detail above in connection with the definitions of R2, R3, and R4. Likewise, the term xe2x80x9cheteroarylxe2x80x9d means those groups which are illustrated in more detail above in connection with the definitions of R2, R3, and R4.
With the exception of the use in accordance with the invention of the modified hydrogenation catalyst, the hydrogenation process can be carried out under hydrogenation conditions which are known per se, especially with respect to solvent, temperature, pressure, amount of hydrogenation catalyst as well as duration of the hydrogenation reaction. However, in order to arrive as selectively as possible at the respective primary amine, the hydrogenation is preferably carried out in pure ammonia or in mixtures of ammonia and an organic solvent which are known per se for this purpose. Suitable organic solvents in such mixtures are those mentioned above in connection with the dispersion medium.
Also, the isolation and the purification of the respective hydrogenation product can be carried out according to methods known per se.